Generator, transmission and distribution transformers are some of the most critical and expensive assets in a power network. Moisture is a necessity in cellulose materials, but too much is absolutely detrimental to the service life of power transformers. Moisture, more specifically excessive moisture, has been enemy number one in power transformers utilizing cellulose insulation with insulating oil for a long time.
In modern day networks transformers are increasingly over stressed due to power demands. These instances have a habit of occurring at higher rates of change than in the past. The impact of this, on a transformer deemed ‘wet’, is a higher possibility of failure. This is primarily due to moisture being driven out of the cellulose faster than what the mineral oil can absorb creating a very low dielectric (voltage withstand) in confined spaces in the windings. The consequences are normally catastrophic. Ageing and degradation in power transformers create moisture, acid and sludging, all contributing to weakening the insulating system, thus increasing the risk of shortening the normal service life.
KVTEK developed a system (MAS10) that would remove moisture continuously in a gentle manner. A unique molecular sieve technique is applied to continuously remove moisture and particles from the transformer oil.
System Description
The MAS10 complies fully with IEEE Standard C57-140 – 2006, section 7.2 Guide for the evaluation and Reconditioning of Liquid Immersed Power Transformers. The system continuously circulates transformer oil and dries it through moisture adsorption by a molecular sieve granular adsorbent material contained in the cylinders. The transformer oil is circulated through the system without heating by a small electric pump and remains at the same temperature and pressure conditions as the transformer. By constantly reducing the level of water contained within the oil, water contained within the solid insulation, where over 95% of the water is trapped, will migrate into the oil to maintain the natural water equilibrium. In this way water gradually moves from the solid insulation, to the oil, and then trapped by the molecular sieve.
A particulate filter prevents particle carry-over to the transformer. MAS10 is designed to be a slow, non-invasive, gradual process that will over a period of time, reduce the water contained within the solid insulation, and therefore reduce the rate of ageing, and extend the life of the transformer.
MAS10 system has the capacity to remove approx. 10 liters of water from a transformer before saturation, but the rate at which it will absorb water will depend on many factors, mainly, how much water is available in the oil, and the temperature range through which the transformer will operate. The design flow rate of the pumped oil is nominally 90 litres per hour to give maximum absorption through the molecular sieves.
Operation and Maintenance
MAS10 operates in an external location on a continuous basis with the transformer on-line. It is constructed of stainless steel so needs no additional protection. The pump is a totally immersed canned rotor type, designed for continuous operation. Although the electrical connection box has a rating of IP45 the stainless steel cover offers total environmental protection for the pump, which increases the rating to IP65. MAS cylinders will continue to absorb water from the oil until saturation occurs.
MAS10 has option for permanently mounted moisture monitor taking readings from the inlet and outlet bypass valves. To measure the degree of saturation a reading of ppm water in oil must be taken from both the input and output and compared. When the molecular sieves are new and dry, the reading at the output will be far less than the reading at the input, because the oil will have had its water removed during the pass over the molecular sieves. However, when the molecular sieves saturated, the reading at the output will be very similar to that at the input and requires regeneration.
When the cylinders are found to be saturated they must be replaced. KVTEK offers a cylinder exchange where we supply previously ‘regenerated cylinders to fit in place of the existing ones. This is done by simply using the quick fit couplers on the top and bottom of each cylinder, and removing each cylinder in turn. The couplers self-seal, so there is no oil loss. The replacement cylinders are then fitted and the quick couplers snapped shut. At the same time the particulate filter should also be changed.
Application
New Transformers
After manufacture, the total moisture content in new transformers is typically less than 0.5%. MAS maintain this moisture content and eliminate moisture buildup.
Repaired Transformers
After a major overhaul in a workshop, and after having undergone a vapor-phase treatment, the moisture content of a repaired transformer is similar to that of a new transformer (< 0.5%). Therefore, the application is the same as for new transformers.
In-Service Transformers
Transformers, irrespective of age, should be fitted with a MAS10 to reduce the moisture in the transformer and eliminate moisture buildup. Transformers that have been in service for many years typically have high moisture content (2% and beyond). The objective is to reduce the moisture content of the paper insulation to an acceptable level and then maintain that level. This will substantially increase the life of the transformer.
Option 1: MAS10E
Upon selection of this option you will get the complete system is duly fitted inside the IP 55 enclosure instead of being mounted on the SS Frame.
Option 2: MAS10A
Additionally allows automatic switching of oil circulation pump and giving alarms
With this option conventional MAS10 unit gets integrated with PLC unit and is designated as MAS10A which monitors the moisture level of inlet valve (IN ppm) and outlet valve (OUT ppm) oil flowing through MAS by turning ON/OFF electrically operated oil flow valves. The time duration of inlet and outlet monitoring is user selectable.
If the difference between IN ppm and OUT ppm is below a user settable value, the pump is stopped and a potential free contact is energized which can be configured to generate an alarm.
Additionally if IN ppm falls below some user settable value, pump is turned OFF and another potential free contact is energized which can be used to generate another alarm.
The above sequence is repeated after periodically after set time.
Option 3: MAS10-H2M
Additionally allows monitoring of H2 gas besides automation
MAS can also be supplied with H2 gas monitoring Module TM1 of Serveron make. Technical details of this Hydrogen monitoring device is available in TM1 catalogue.
In addition to the two alarms for moisture level, a third alarm is energized if H2 level increases beyond a value set by the use.
